The invention relates to metal bonded abrasive tools, in particular, diamond dressing tools used to recondition abrasive wheels, and to a novel bond composition which allows for improved mechanical strength and improved abrasive grain retention in the abrasive tools.
To meet the demands of industrial manufacturers, continuous improvements in abrasive retention, bond durability and tool life are a necessity for metal bonded superabrasive tools. Along with the quality of the abrasive grinding tool, the quality of the dressing tool used to recondition the abrasive grinding tool is critical to achieving the desired grinding operation efficiencies and tolerances.
Diamond blade dressers or rotary dressing wheels are used for reconditioning the surfaces of, or generating a profile in grinding wheels. A rotary dresser is used primarily to generate or maintain the shape of abrasive tools having a profiled grinding face. The metal bond composition used in the dressing tool has an enormous impact on dressing tool quality. Metal bonded dressing tools known in the art generally comprise diamond abrasive grain bonded by zinc containing alloys, copper-silver alloys, cobalt alloys, copper, or copper alloys.
Although zinc containing alloys are known for superior bond qualities in metal bonded diamond dressers, they also are known to present disadvantages in manufacturing operations. Zinc is excessively volatile at temperatures used during manufacture of the bonded abrasive tools, resulting in loss of zinc from the bond. This raises the liquidus temperature of the metal bond resulting in the need for a higher manufacturing temperature. The higher temperature further leads to premature furnace lining failure, higher energy costs and potential environmental liabilities.
A near-eutectic copper phosphorus composition described in U.S. Pat. No. 5,505,750 is used in a metal bond for dressing tools. The bond also comprises hard phase particles, such as tungsten, tungsten carbide, cobalt, steel, sol gel alpha-alumina abrasive grain and stellite.
The rotary dressers described in U.S. Pat. No. 3,596,649 are made with a metal powder bond composition comprising tungsten carbide coated diamond grits bonded within in a cobalt matrix. It is theorized that the observed improvements in this tool are due to the relative ease with which the materials adjacent to the diamond grit abrade during use to expose fresh diamond facets for dressing. The previously known 50/50 mixtures of tungsten carbide/cobalt are characterized as yielding a tough matrix immediately adjacent the diamond, resulting in less efficient cutting action.
Abrasive grinding tools described in U.S. Pat. No. 5,385,591 are made with a metal bond comprising a filler with a specified hardness value. The filler consists of certain grades of steel or ceramic. The filler is sintered into the bond, together with the abrasive grain and copper, titanium, silver or tungsten carbide. Preferred bond compositions contain silver, copper and titanium, with the titanium being used to form copper-titanium phases in the sintered bond.
A metal braze composition for a monolayer abrasive tool is described in U.S. Pat. No. 5,492,771 as comprising an alloy or mixture of silver, copper and indium with titanium or other active metal to wet the abrasive grain.
A metal bond for either a monolayer abrasive tool or a metal matrix bond abrasive tool is described in U.S. Pat. No. 5,011,511 as comprising copper silver titanium alloys, or copper titanium alloys, or copper zirconium alloys, copper titanium eutectics and copper zirconium eutectics. During bonding the abrasive grain and the bond components react to form carbides or nitrides.
A nickel alloy bond for rotary dressers formed by an electrolytic plating process is described in U.S. Pat. No. 4,685,440.
Despite the development of these metal bond systems for abrasive tools, there remains a demand for better bonds characterized by a longer tool life, better resistance to abrasion and better abrasive grain bonding.